1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to a semiconductor device having a substrate contact and a method of manufacturing the same.
2. Description of the Related Art
To meet the recent demands for a higher speed and lower power consumption of semiconductor devices, vigorous developments in semiconductor devices using a silicon-on-insulator (SOI) wafer are in progress. The SOI wafer has a thin semiconductor layer formed on a support substrate via an insulating layer called a buried oxidation (BOX) layer.
In the SOI wafer, the thin semiconductor layer of a transistor is always floating due to the presence of the insulating layer. Since the SOI wafer has advantages that, e.g., the parasitic capacitance of the transistor is low and complete element isolation is possible, its substrate structure is suitable for a higher speed and lower power consumption of semiconductor devices.
Unfortunately, the state in which the semiconductor layer is always floating makes the transistor susceptible to the substrate floating effect to result in the occurrence of the kink phenomenon and a decrease in drain breakdown voltage. To solve this problem, a contact from the thin semiconductor layer to the support substrate is formed to fix the potential of the support substrate itself, thereby suppressing potential fluctuation of the thin semiconductor layer (e.g., see Jpn. Pat. Appln. KOKAI Publication No. 2002-190521).
A semiconductor device manufacturing method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-190521 comprises steps of forming a first opening extending through an SOI layer and an insulating layer and reaching a substrate, burying polysilicon in the first opening to form a low-resistance plug layer by ion implantation, forming an interlayer dielectric film on the SOI layer and plug layer, and forming, in the interlayer dielectric film, a second opening reaching the plug layer.
With these steps, impurity ions are sufficiently implanted into the silicon substrate at the bottom of the substrate contact hole. In addition, a substrate contact hole and a contact hole of the transistor formed on the SOI layer, which have different depths, are formed at the same time.
However, the semiconductor device manufacturing method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-190521 increases the number of steps to form a plug layer. This may decrease the productivity to result in an increase in the manufacturing cost of a semiconductor device.
That is, this method requires a significantly higher manufacturing cost of an SOI substrate as compared with a bulk semiconductor substrate. To form a semiconductor device on the SOI substrate, it is necessary to decrease the manufacturing cost of the semiconductor device by simplifying the process involved as much as possible.